Improve poor security recommendation in docs

As reported in #9960, the current documentation recommends an insecure practice for
key generation from a password (a single round of SHA-256). The modified documentation
uses ActiveSupport::KeyGenerator to perform proper key stretching.
fixes warning in the AR test suite
ActiveRecord -> Active Record
better document `next_week` functionaility closes #9568
Delegation method bug
Add documentation and test to delegation method that make sure we're
aware that when a delegated object is not nil or false and doesn't
respond to the method it will still raise a NoMethodError exception.
Merge pull request #10347 from lellisga/delegation_bug_documentation

Delegation method bug
formatting
Merge pull request #10351 from JonRowe/update_as_date_next_week_to_document_intent

Propose better documentation for ActiveSupports `next_week` functionaility
Merge pull request #9980 from stouset/patch-1

Improve poor security recommendation in docs

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